It is known to adapt vehicles such as conventional highway tractors for use on rails by providing retractable rail wheels which are lowered to maintain the position of the vehicles on the railway tracks and are raised for road use of the vehicle.
For example, U.S. Pat. No. 5,103,740 to Masse discloses a vehicle for road and rail operation where both road and rail wheels are driven. An adjustable suspension can be used to vary the proportion of the vehicle weight carried by the rear rail wheels and rear road wheels when in the railway configuration. In wet conditions, in which rubber gives poor traction on steel rails, the proportion of weight carried by the rail wheels is increased such that a greater proportion of driving force and braking force are supplied through the cast iron rail wheels.
U.S. Pat. No. 5,868,078 to Madison discloses a road/rail vehicle that is street legal, but also provides sufficient power to move freight cars on low density rail lines or at other desired locations. The vehicle has a transfer case to provide front wheel drive by road wheels when the vehicle is in a road or highway mode and to provide rear wheel drive by rail wheels when in a rail mode.
U.S. Pat. No. 5,016,544 to Woollam discloses a convertible road/rail power vehicle with road wheels and retractable front, middle, and rear rail wheels for moving rail cars. Drive is provided by a set of retractable solid rubber rail wheels near the longitudinal center of gravity near the middle of the vehicle and an adjustable air bag suspension allows the amount of vehicle weight carried by the middle drive wheels to vary the tractive weight exerted on the drive wheels. The rubber rail wheels are raised for road use.
U.S. Pat. No. 6,976,432 to Jacob discloses a railcar moving vehicle with retractable rail wheels for guiding the vehicle on rails, and rubber-tired drive wheels that provide drive for both road and rail use. The rubber-tired drive wheels are configured to support the vehicle on a roadway in highway mode, and to contact the rails in rail mode such that the same road wheels drive the vehicle in both the rail and road modes. A moveable weight is disposed on a rear portion of the frame and a load-shifting mechanism moves the moveable weight between a rearward position for rail mode to provide increased tractive weight on the driving road wheels contacting the rails, and a forward position for highway mode.
Brandt Road Rail Corporation of Regina, Canada manufactures road/rail vehicle with front and rear rubber road wheels and front and rear retractable steel rail wheels where, like the Jacob vehicle described above, the rubber rear wheels provide drive for both road and rail use. In rail mode the front rail wheels are lowered and the front road wheels raised above the rails. An air bag suspension controls the proportion of vehicle weight that is carried by the rear rail wheels and the rear drive wheels. The tractive weight carried by the drive wheels provides the traction between the wheels and rails to allow the necessary propelling force to be exerted on the rails. When starting out under a heavy load the maximum tractive weight is on the rubber drive wheels with therefore reduced weight on the rear rail wheels. As the vehicle and load starts to move, the required propelling force reduces, and as the speed increases the operator manipulates a valve control connected to the air bag suspension to increase the downward force on the rear rail wheels, reducing the tractive weight on the drive wheels.